A well-known refrigeration cycle is a closed loop system in which refrigerant, the working fluid, is compressed by a compressor that increases the pressure of the refrigerant gas. The compressor is driven by a motor that is controlled by a control panel. High pressure refrigerant from the compressor is discharged through the compressor discharge which is in fluid communication with a condenser that condenses the high pressure gas into a pressurized fluid. In one embodiment, the compressor is a centrifugal compressor. Alternatively, the compressor may be a reciprocating, rotary, scroll, or screw compressor.
The condenser is in heat exchange communication with a first heat transfer medium that removes heat of condensation from the refrigerant, resulting from the change of state of refrigerant from hot, high pressure gas to liquid. This heat transfer medium may be the atmosphere (air or forced air) or a liquid, preferably water. The various ways of removing this heat are well know and do not contribute to the inventive nature of this invention. The condensed refrigerant from the condenser is in fluid communication with an expansion device that expands at least some of the pressurized fluid into a gas as it flows within the closed loop refrigeration system. The closed loop system from the discharge of the compressor to the expansion valve is termed the high pressure side of the refrigeration system or circuit.
After the refrigerant exits the expansion device as a mixture of gas and liquid, its pressure is reduced. The evaporator receives the refrigerant with lowered pressure from the expansion device. The evaporator is in heat exchange communication with a second heat transfer medium. The refrigerant in the evaporator absorbs heat from the second heat transfer medium as the liquid portion of the refrigerant undergoes a change of state to a vapor. As this heat is absorbed, the heat transfer medium is cooled. The heat transfer medium may be used directly to cool or refrigerate an area, for example when the heat transfer medium is air, or it may be used to cool a liquid, such as water and conveyed to another heat transfer device in an area or room, such as in chilled water applications. In such applications, the chilled water is sent to heat transfer devices in separate areas of a building on demand. The refrigerant gas from the evaporator is then returned to the suction side of the compressor to complete the circuit. The closed loop system between the expansion device and the suction side of compressor is termed the low pressure side of the system circuit.
A motor operates the compressor. The motor used with the compressor can be powered by a variable speed drive (VSD) or can be powered directly from an alternating current (AC) or direct current (DC) power source. The motor may include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source. The motor can be any suitable motor type, for example, a switched reluctance motor, an induction motor, or a permanent magnet motor.
The electric motor that operates such compressors typically includes a housing, a rotor and a stator. The housing generally provides a hermitic seal for the motor. Electrical power operates the stator that in turn causes the rotor to rotate. A shaft from the compressor is connected to the motor rotor, which rotates the compressor. The power provided to the stator generates significant heat in the motor, which must be cooled to prevent overheating and damage. Various cooling schemes have been used to cool these motors, including water jackets circulating cooling water around the motor.
The trend in modern compressors is to utilize electromagnetic bearings to support the rotor. These electromagnetic bearings also draw power for operation from the power supply and also may generate significant heat that requires removal from the system.
What is desired is a cooling scheme to remove excess heat from a motor and from electromagnetic bearings and their controls utilized with a compressor. Ideally, the cooling circuit should utilize fluid already used with the refrigerant circuit.